The present invention refers to an ejector, of the kind used in plastic injection moulds, aluminium, bakelite or any other material, and which, parallel to its function as such, is conceived of as a complement moulder of small negatives, allowing for an easy mould release of such negative zones at the same time as it facilitates the extraction of the part to obtain in the mould cavity.
When it comes to moulding a specific part it is frequent that in the same recesses or orifices exist, that is to say xe2x80x9cnegativesxe2x80x9d which would make the mould release impossible with regard to the utilization of single-piece semi-moulds, for which it is necessary to resort to progressive moulds in which different parts of the same are movable in different directions, with the aim of freeing the negatives from the part to be obtained.
This entails the need to use bulky moulds, expensive to carry out and maintain, and with a poor performance in view of the slowness of the mould release.
Trying to obviate this problem the applicant himself is the holder of Spanish utility model U 95021186, in which a mould-ejector accessory for injection moulds is described, which turns out to be particularly ideal in the case of relatively small negatives as, being conveniently implanted in the corresponding mould cavity in the right number and configuration, it practically takes up the space of conventional ejectors, operating like them and bringing about the freeing of the negatives in the ejection manoeuvre itself of the part to be obtained.
More specifically, such accessory is structured with an elongated steel body, in which a rod equipped with fixing means to the ejecting plate and which resembles a conventional ejector, through a flat and elastically deformable neck connects to a head which plays in a housing formally and dimensionally coincident with it, operatively established in the mould, this latter head being affected by a recess in the material in turn adapted formally and dimensionally to one of the small negatives which participate in the part to be obtained.
Thus, at the end of the injection phase in the ejecting plate movement itself, as well as the conventional ejector being dragged, so are the accessory or accessories integrated to the mould, so that parallel to the pushing movement on the moulded part, its head leaves the corresponding mould housing, automatically generating a side deformation of said head which gives rise to the freeing of the corresponding negative.
This solution, while it is totally acceptable from a theoretical point of view, in practice presents problems which centre fundamentally on two aspects:
The parts to be machined, both the moulder-ejector accessory and the mould are formally complex, as the head of the accessory is over-sized with regard to the constituent sector of the rod and moreover adopts a configuration which is detached from the cylinder, the configuration having to be extended to the mould itself, which obviously entails complex machining operations.
As a result of the complexity of shapes mentioned it is difficult to achieve a perfect fitting between the moulder-ejector accessory and the mould itself, with the risk of the mould material penetrating the interstices generated among these elements, which makes the parts to be obtained defective, causing the mould""s deterioration which has to be periodically disassembled for cleaning.
Expandable ejectors are also known with the same complementary moulding function, whose head configures as a frusto-conical of a double conicity pincer, with diametric cuts which allow the same to expand and in the cavity of whose cuts the housing for the negative is established, so that in this case the mould body does not take part in the conformation of said negative, but the manufacturing processes of these conic sections are also very costly, and also the help of a bushing which, conveniently implanted in the mould, works as a guide and closing component for the moulder-ejector head.
In the Spanish application for utility model number 9103746, of the same holder, a fastening head is described therein for ejectors and tubings in injection moulds, and more specifically the special structuring of said head, with which a quick assembly and disassembly of the ejector itself is feasible, as well as a perfect fixing of the same, both in axial direction and angular direction, in operative condition.
The expandable ejector that the invention proposes satisfactorily solves the problem previously explained, determining, parallel to an optimum functioning, a clear simplification in its constructive process, with the consequent reduction in cost that it entails.
For this and in a more specific way said expandable ejector centres its features on the fact that its head is cylindrical and coincident in diameter with the majority sector of the same constituent of the rod which by its free end receives the ejector base.
Thus the mould housing for the ejector is perfectly cylindrical, which entails an extremely simple machining process, and the expandable ejector is obtained starting from a steel rod, also cylindrical, in which it is only necessary to make the cuts of its head to achieve the pincer effect in its subsequent tempering, and the side recesses to facilitate the elastic deformability of said pincer, which are also obtained in the extremely simple machining process.
On the other hand, and as it is to do with a cylindrical component and a housing which is also cylindrical, the fitting between both parts is perfect.
The ejector will be marketed only with the cuts in its head, which converts it into a pincer, each user being the one who makes the drawing in negative in the inside of said head corresponding to the practical use intended for the ejector. Furthermore, the ejector will also be supplied over-sized in length, as its coupling to the ejector base permits the surplus sector in each case to be cut from the corresponding end, also for the ejector as a whole to suit the specific demands of every user.
Thus structured, the expandable ejector can function perfectly well without the classical bushing-guide, but may optionally be assisted by said bushing in order to avoid wearing away in the mould produced by friction.